1. Field of the Invention
This invention relates to a method for bonding rubber to adhesives.
2. Description of the Prior Art
Many treatments of polyolefin and hydrocarbon rubber surfaces to improve their joinder to dissimilar materials such as epoxy, polyurethane, polyester and acrylic are well known. For example, polyhydrocarbon materials are prepared for adhesive bonding by sulfuric acid etching photosensitized oxidation, flame oxidation, halogenation corona or glow discharge, gamma, ultraviolet or electron irradiation, graft copolymerization and other methods of chemical modification of the surface. These methods all introduce polar chemical groups into the non-polar polyhydrocarbon and increase such forces of adhesion as hydrogen bonding and dipole interactions. In addition the treatments may increase the surface area for bonding or may chemically crosslink the surface to be bonded, thus eliminating cohesively weak surface layers. However, hydrogen bonding and dipole interactions are an order of magnitude weaker than true covalent chemical bonds. Furthermore these adhesive forces are disrupted completely as soon as moisture penetrates along the bond line and adhesive failure results. The graft copolymerization techniques do allow the possibility of covalent chemical bond formation but require an additional lengthy step in the process.
Concentrated acid etching, oxidation, and radiation treatments particularly in the presence of oxygen also can provide the possibility for covalent bond formation with adhesive, but these drastic treatments also break covalent bonds near the rubber surface resulting is stressed and often brittle layers.